MECHANICAL PROPERTIES AND WATER · PDF filepolyethylene (rHDPE) /natural rubber (NR) blends...

PEER-REVIEWED ARTICLE bioresources.com

Viet Cao et al. (2011). “rHDPE/NR/KP biocomposites,” BioResources 6(3), 3260-3271. 1

MECHANICAL PROPERTIES AND WATER ABSORPTION OF KENAF POWDER FILLED RECYCLED HIGH DENSITY POLYETHYLENE/NATURAL RUBBER BIOCOMPOSITES USING MAPE AS A COMPATIBILIZER Xuan Viet Cao,a Hanafi Ismail,a,* Azura A. Rashid,a Tsutomu Takeichi,b and Thao Vo-Huu c

The performance of kenaf powder (KP) filled recycled high density polyethylene (rHDPE) /natural rubber (NR) blends with and without a compatibilizer, maleic anhydride grafted polyethylene (MAPE), were investigated. The composites with different filler loading (0 to 40 phr) were prepared with a Haake internal mixer. Increasing the KP loading in rHDPE/NR/KP biocomposites reduced the tensile strength and the elongation at break but increased the stabilization torque and the tensile modulus. The addition of MAPE as a compatibilizer increased the tensile strength, elongation at break, and modulus of the composites. This might be attributed to the enhanced adhesion between the filler and polymer matrix, as evidenced from the morphology, using scanning electron microscopy. The incorporation of compatibilizer also reduced the water absorption of the composites.

Keywords: Recycled HDPE; Kenaf; Biocomposites; Mechanical properties; Water absorption; Compatibilizer Contact information: a: School of Materials and Mineral Resources Engineering, Engineering Campus, Universiti Sains Malaysia, 14300, Nibong Tebal, Penang, Malaysia; b: Department of Environmental and Life Sciences, Toyohashi University of Technology, Japan; c: Department of Polymer Materials, Faculty of Materials Technology, Ho Chi Minh University of Technology, Viet Nam; *Corresponding author: [email protected] INTRODUCTION

Remarkable attention has been paid to thermoplastic elastomers (TPEs) from both practical and scientific points of view. Due to their unique microstructure, TPEs are promoted for their attractive elastic properties at room temperature, their flowability at high temperature, and their ability to be remelted for recycling use (Ismail et al. 2001b). A further benefit of TPEs is that they provide high value-added products if the components are derived from waste sources (‘upcycling’) (Grigoryeva et al. 2004).

The incorporation of various types of filler into a TPEs matrix has been carried out either to improve properties or further reduce the cost of materials or to achieve both objectives simultaneously. Recently, fillers (bio-fibers or powders) derived from renewable natural resources such as banana, sisal, hemp, jute, pineapple, bamboo, cotton, coconut, rice husk, and kenaf have become strong competitors to inorganic fillers. These fillers offer several advantages including low density, low cost, relative non-abrasiveness, high filling levels, recyclability, biodegradability, and renewable nature (Bledzki et al. 1999). Kenaf (Hibiscus cannabinus) is well known as a cellulosic source having econ-



omical and ecological advantages. Kenaf is widely used as an alternative raw material to wood in the pulp and paper industries for avoiding destruction of forests and also used as non-woven mats in the automotive industries, textiles, fibreboard (Nishino et al. 2003; Ashori 2006; Ashori et al. 2007). For the last few years, many studies have been reported on the utilization of kenaf as reinforcement material for polymeric composites (plastics as well as elastomers). However, as far as TPEs are concerned, very limited studies have been made on the use of kenaf core powder as a filler in HDPE/NR composites.

The mechanical properties of TPEs composites are dependent strongly upon dispersion of the filler in the matrices and the adhesion at the filler/matrix interface. Because of its hydrophilic nature, the filler does not wet or interact with hydrophobic polymers due to the difference in surface energies (Buggy et al. 2005). It is necessary to use compatibilizers to improve the compatibility between fiber and matrix. Many researchers (Oksman et al. 1998; Felix et al. 1991; Mohanty et al. 2006; Han et al. 2008) have shown that the interaction at the fiber-matrix interface can be improved by adding a small amount of a grafted matrix. Among the different compatibilizers, maleic anhydride is the most commonly used.

In this study, kenaf core powder was used as a filler to produce biocomposites based on recycled HDPE/natural rubber blend. The effect of filler content and a compatibilizer, maleic anhydride grafted polyethylene (MAPE), on the mixing, tensile properties, and water absorption of the reinforced biocomposites was investigated. EXPERIMENTAL Materials

rHDPE was obtained from Zarm Scientific and Supplies Sdn Bhd, Penang with melt flow index of 0.237 g/10 min (at 2000C and 5 kg load). Natural rubber used was SMR L grade from the Rubber Research Institute of Malaysia (RRIM). MAPE with appropriately 3 wt% level of grafting was supplied by Aldrich Chemical Company, Inc. (Milwaukee, WI). Kenaf powder was produced by grinding kenaf core in a table-type pulverizing machine and sieved to obtain the powder size in range of 32 to 150 µm. Compounding and Processing

Formulations of KP filled rHDPE/NR composites are given in Table 1. Prior to compounding, rHDPE and KP were dried by using a vacuum oven at 80oC for 24 h. The composites were prepared by melt mixing using an internal mixer at 165oC with the rotor speed of 50 rpm. The rHDPE was first charged into the mixer and melted for 3 min. NR was added at third minute. The MAPE and KP were added at sixth min, respectively. The blend was allowed to further mixing for another 6 min to obtain the stabilization torque. The total mixing time was 12 min for all samples. The composites were then compression-molded at 165oC into 1 mm sheets for preparing test samples.

Tensile Measurement

The tensile properties were measured using an Instron 3366 machine at a cross-head speed of 50 mm/min at 25 ± 3oC according to ASTM D 412. Tensile strength,



tensile modulus and elongation at break of the each sample were obtained from the average of five specimens.

Morphology Study

The tensile fracture surface was investigated with a Supra-35VP field emission scanning electron microscope (SEM). The samples were coated with gold/palladium by a sputter coating instrument (Bio-Rad Polaron Division) for 45 minutes to prevent electro-static charging during evaluation. Water Absorption

A water absorption test was carried out by immersing the samples in distilled water at room temperature (25oC). The water absorption was determined by weighing the samples at regular intervals on an electronic balance. The percentage of water absorption, Mt, was calculated by,

Mt = 100 x (wt – wo)/wo (1)

where wo and wt are the original dry weight and weight after exposure, respectively. Table 1. Formation of KP filled rHDPE/NR biocomposites*

Materials Composition (phr)

Recycled high density polyethylene (rHDPE) 70

Natural rubber (SMR L) 30

Kenaf powder (KP) 0, 10, 20, 30, 40

MAPEa 5

Note: (phr)-part per hundred resin a 5% of KP * Similar biocomposites but without MAPE were also prepared.

RESULTS AND DISCUSSION Mixing and Stabilization Torque

The torque-time curves of composites are shown in Fig. 1. A similar pattern of torque curves was observed for all composites (except for the control sample). There were three torque increments due to the material loading. An initial torque increase and the second one at the third minute were detected corresponding to rHDPE and NR charging, respectively. The last was registered for addition of KP. These maximum torques after rHDPE and NR addition showed a decreasing trend from 0KP to 40KP due to the decrease of polymer matrix quantity used for mixing. In contrast, the third maximum torque increased from 10KP to 20KP, 30KP, and 40KP due to the higher filler loading in composites. There was a decrease in torque observed at the sixth minute, which originated from the addition of MAPE. The decrease was shown from 10KP to



40KP, reflecting the dosage of MAPE in composites. This was because MAPE acted as an external lubricant, which reduced the viscosity of compounds as the time it added (Liu et al. 2003). Upon completion of filler dispersion, the torque started to decrease gradually, which might be due to a reduction in viscosity as the stock temperature increased.

Figure 2 shows the stabilization torque at the end of mixing stage (12 min) of rHDPE/NR/KP biocomposites with and without MAPE. It can be seen that stabilization torque increased gradually with increasing filler loading. This was due to the higher the filler content the higher the interfacial interactions occurred between filler and matrix, which caused the reduction of the mobility of polymer chains and thus increased the viscosity and stabilization torque (Ismail et al. 2001b). The addition of MAPE resulted in the higher stabilization torque in the compatibilized composites, which improved the filler-matrix interfacial bonding, leading to an increase of viscosity of the mixtures.

Fig. 1. Torque development for rHDPE/NR/KP biocomposites with MAPE as a compatibilizer

Fig. 2. Stabilization torque at 12 min of rHDPE/NR/KP biocomposites

0

5

10

15

20

25

0 2 4 6 8 10 12

To

rqu

e (N

m)

Time (min)

0 KP 10 KP 20 KP30 KP 40 KP

56789

101112131415

0 10 20 30 40

To

rqu

e (N

m)

Filler content (phr)

Without MAPE

With MAPE



Tensile Properties Figure 3 shows the effect of KP content on tensile strength of the rHDPE/NR/KP

biocomposites. Tensile strength dropped with the incorporation of KP. The reduction of tensile strength might be due to poor adhesion between KP and matrix. In addition, the other reason was the irregular shape of KP, because of which their capability to support stress transmitted from the polymer matrix is rather poor (Fig. 4). The decreasing trend in tensile strength could be also explained by the agglomeration of filler particles and dewetting of the polymer at the interphase (Ismail et al. 2001a).

The addition of MAPE showed higher tensile strength for the rHDPE/NR/KP biocomposites. Percentage increase in tensile strength was between 6% and 9.6%. The results could be explained in term of the better adhesion at the fiber-matrix interface due to the presence of compatibilizer, as shown later in morphology study. The interfacial adhesion was improved through forming hydrogen bonding between succinic anhydride moieties from MAPE and hydroxyl groups on the KP surfaces (Lu et al. 2005). The better interfacial bonding reduced the interfacial stress concentration and might prevented fiber-fiber contact.

Fig. 3. Tensile strength versus KP content of rHDPE/NR/KP biocomposites

The tensile modulus of rHDPE/NR/KP biocomposites, with and without MAPE increased with increasing filler loading, is shown in Fig. 5. The addition of KP was expected to increase the modulus resulting from the inclusion of rigid filler particles in the soft matrix. However, at a similar filler loading, composites with MAPE exhibited higher tensile modulus than those without MAPE. Increase in tensile modulus varied between 4.5% and 12.3%. Again, this might be due to better interactions between matrix and filler with the presence of MAPE.

0

2

4

6

8

10

12

14

16

18

0 10 20 30 40

Ten

sile

str

eng

th (

MP

a)


Without MAPE With MAPE

PEER-

Viet C

Fig. 4

Fig. 5 biocorHDPto thefiller

REVIEWED ART

Cao et al. (201

4. SEM microg

5. Tensile mod

Figure 6 omposites wPE/NR blende decreased pand the mat

0

100

200

300

400

500

600

700

800

Mo

du

lus

(MP

a)

TICLE

11). “rHDPE/N

graph of irreg

dulus versus

depicts thewith filler cod resulted inpolymer chatrix. With th

0

Without

With MA

NR/KP biocom

gular morpholo

KP content o

e variationontent. It cann a reductionain mobility he addition o

10

MAPE

APE

mposites,” Bi

ogy of kenaf

of rHDPE/NR/

of elongatin be seen thn of elongati

or deformabof MAPE, e

20

Filler conten

biore

ioResources

powder

/KP biocompo

on at breakhat the incoion at break.bility of a ri

elongation at

30

nt (phr)

esourc

s 6(3), 3260-3

osites

k of the rHrporation of. This mightgid interfacet break of th

40

ces.com

3271.

HDPE/NR/Kf KP into tht be attributee between thhe composite

m

6

KP he ed he es



was enhanced. It was found that the enhancement was strongly dependant on filler content. At 10 KP, the increment was 161%. However, it was 78.8% for 20 KP and lesser 35% for 30 KP and 40 KP. In compatibilized composites, better filler dispersion and good adhesion between filler and rHDPE/NR matrix were obtained, which would enhance the stress transfer from the matrix to the filler phase. However, at high filler loading, the stress propagation from matrix to filler was obstructed because of the irregular morphology of KP. This hindered the filler orientation during tensile test and resulted in the deterioration of elongation of the composites, especially, after 20 KP. In addition, the tensile failure was due mainly to fiber-matrix delamination, hence, lowered elongation of the composites. MAPE seemed to be less effective for elongation at break of the composites when the weight ratio of the matrix and KP reduced.

Fig. 6. Elongation at break versus KP content of rHDPE/NR/KP biocomposites Water Absorption

Figure 7 shows the water absorption of uncompatibilized KP filled rHDPE/NR biocomposites as a function of immersion time. Obviously, the water absorption increased with increase in filler content. Natural fibers are highly hydrophilic in nature and are permeable to water. Incorporation of lignocellulosic filler into polymeric composites thus generally increases the rates of water sorption ability by forming hydrogen bonding between water and the hydroxyl group of cellulose, hemicellulose in the cell wall. As filler content increased, the number of hydrogen bonds between organic components and water molecules also increased. Higher filler content resulted in higher voids entrapped leading higher water accumulating at the interface between the fiber and the matrix (Jacob et al. 2005). Figure 8 presents the variation of water uptake at 63 days with filler content for uncompatibilized and compatibilized rHDPE/NR/KP biocomposites. The water absorp-

0

50

100

150

200

250

300

350

400

10 20 30 40

Elo

ng

atio

n a

t b

reak

(%

)


Without MAPE

With MAPE

Eb for 0 phr KP = 607 %



tion is dependent on the availability of free –OH groups on the surface of the fiber. In compatibilized composites, the number of –OH groups could be reduced via the esterification between MAPE and –OH of fiber. Therefore, the absorption of water became restricted (Naik et al. 2007). In addition, the voids in compatibilized composites were less due to the improvement of interfacial filler/matrix adhesion, which limited the penetration of water molecules into the composites.

Fig. 7. Water absorption versus immersion time of uncompatibilized rHDPE/NR/KP biocomposites

Fig. 8. Equilibrium water uptake at 63 days of rHDPE/NR/KP biocomposites with and without MAPE

0

2

4

6

8

10

12

14

16

18

20

0 10 20 30 40 50 60

Wat

er u

pta

ke (

%)

Time (days)

0 KP 10 KP 20 KP

30 KP 40 KP

0

4

8

12

16

0 10 20 30 40

Wat

er u

ptak

e(%

)


Without MAPE With MAPE

PEER-

Viet C

Morp

surfafilledand (fibrilwas mmannaggloFurthevidestrengcomp Fig. 9phr, (b

Figurwith fractubetteragglo

(a)

REVIEWED ART

Cao et al. (201

phology Scanning

ce of rHDPEd rHDPE/NR(c), respectivlation and dmore visiblener and mosomeration. Shermore, voences of poogth and elonposites with h

9. SEM microgb) 30 phr, and

The incorre 10 (a), (b)MAPE at 1

ures and highr fiber-matriomeration). T

TICLE

11). “rHDPE/N

electron mE/NR/KP bioR biocomposvely. It can bdeformed in e. As shown st of the KSome of fiids were al

or interfacial ngation at bhigher filler

graphs of rHDd (c) 40 phr

rporation of ), and (c) sh10phr, 30phher tougheniix adhesion rThe adhesio

(c)

NR/KP biocom

icroscopy (Socompositessites at 10, 3be observedductile modin Figure 9(

KP fibers dirbers were lso present,adhesion be

break as welloading.

DPE/NR/KP b

compatibilizhows the michr, and 40phing effect coresulted in len was strong

Fiber

Void

mposites,” Bi

SEM) was us. SEM micr0, and 40 phthat at lowe

de. At higher(b) and (c), rectly contapulled out as shown etween fiberll as higher

biocomposites

zer improvedcrostructure hr, respectivompared to thess fiber pullg enough so

(b)

pull out

Fiber

biore

ioResources

used to examrographs of thr of KP areer filler contr filler loadifibers were

acted one anor remainein Fig. 9(c

r and matrixwater adso

s (200X) at di

d adhesion oof KP filled

vely. The mhe uncompaling-out and

o that the fib

r pull out

esourc

s 6(3), 3260-3

mine the tethe fracture se shown in Ftent, the saming, the presarranged in nother, thused loosely c). These f. Therefore, rption were

ifferent filler c

of the matrixd rHDPE/NR

morphology satibilized comd fiber-fiber ber was inste

ces.com

3271.

nsile fractursurface of KFig. 9 (a), (bmple had higsence of fibea disoriente

s resulting iwith matrix

features werlower tensil obtained fo

content: (a) 10

x to the fiberR compositeshowed mormposites. Thcontact (filleead broken o

m

9

re KP b), gh er ed in x. re le or

0

rs. es re he er or

PEER-

Viet C

even were the fithe imThis

Fig. 1comp CON

stabilelongwas arHDPthis dadhesto enhthe un

(a)

REVIEWED ART

Cao et al. (201

torn under observed. T

iber and the mprovementproved that

10. SEM microatibilizer at di

NCLUSIONS The inco

lization torqgation at breattributed toPE/NR biocodrawback of sion betweenhancements ncompatibili

TICLE

11). “rHDPE/N

tensile loadThis finding w

matrix (Demt in not onlyMAPE was

ographs of rHifferent filler c

S

orporation oque and theeak of the bo the poor fiomposites wf kenaf filledn hydrophiliin mechanicized biocom

(c)

NR/KP biocom

. Matrix fibwas a strong

mir et al. 200y tensile strean effective

HDPE/NR/KPcontent: (a) 10

of kenaf pe tensile mobiocompositeiller-matrix

was also obsed rHDPE/NRc kenaf fibercal propertie

mposites.

Fiber breakage

mposites,” Bi

rillation toog indication06). The impength and m

compatibili

biocomposite0 phr , (b) 30

powder intoodulus but es. The pooradhesion. H

erved. HoweR biocomposr and the hyd

es and reduct

(b)

biore

ioResources

ok place, andof good inteproved interf

modulus, but izer for this c

es (200X) witphr, and (c) 4

o rHDPE/Ndecreased tr performan

High water aever, the addsites. MAPEdrophobic ption of wate

Fiber breakage

esourc

s 6(3), 3260-3

d more smaerfacial adhefacial adhesialso elonga

composite.

th MAPE as a40 phr

NR blend inthe tensile

nce of ultimaabsorption odition of MAE improved tpolymer matrer absorption

e

ces.com

3271. 1

ller filamentesion betweeion explainetion at break

a

ncreased thstrength, anate propertief kenaf fille

APE overcamthe interfaciarix, which len compared t

m

10

ts en ed k.

he nd es ed

me al ed to



ACKNOWLEDGEMENT

The authors would like to thank AUN/SEED–Net/JICA for the financial support through Collaborative Research (CR) grant. REFERENCES CITED Ashori, A. (2006). “Pulp and paper from kenaf bast fibers,” Fibers and Polymers 7 (1), 26-29. Ashori, A., and Raverty, W.D. (2007). “Printability of sized kenaf (Hibiscus cannabinus) paper,” Polymer-Plastics Technology and Engineering 46 (7), 683-687. Bledzki, A. K., and Gassan, J. (1999). “Composites reinforced with cellulose based fibres,” Progress in Polymer Science 24(2), 221-274. Buggy, M., Bradley, G., and Sullivan, A. (2005). “Polymer–filler interactions in

kaolin/nylon 6,6 composites containing a silane coupling agent,” Composites Part A: Applied Science and Manufacturing 36(4), 437-442.

Demir, H., Atikler, U., Balkose, D., and Tihminlioglu, F. (2006). “The effect of fiber treatments on the tensile and water sorption properties of polypropylene-luffa fiber composites,” Composites Part A: Applied Science and Manufacturing 37(3), 447-456.

Felix, J. M., and Gatenholm, P. (1991). “The nature of adhesion in composites of modified cellulose fibers and polypropylene,” Journal of Applied Polymer Science 42(3), 609-620.

Grigoryeva, O., Fainleib, A., Starostenko, O., Tolstov, A., and Brostow, W. (2004). “Thermoplastic elastomers from rubber and recycled polyethylene: Chemical reactions at interphases for property enhancement,” Polymer International 53(11), 1693-1703.

Han, G., Lei, Y., Wu, Q., Kojima, Y., and Suzuki, S. (2008). “Bamboo-fiber filled high density polyethylene composites: Effect of coupling treatment and nanoclay,” Journal of Polymers and the Environment 16(2), 123-130.

Ismail, H., Nizam, J. M., and Abdul Khalil, H. P. S. (2001a). “The effect of a compatibilizer on the mechanical properties and mass swell of white rice husk ash filled natural rubber/linear low density polyethylene blends,” Polymer Testing 20(2), 125-133.

Ismail, H., Salmah, and Nasir, M. (2001b). “Dynamic vulcanization of rubberwood-filled polypropylene/natural rubber blends,” Polymer Testing 20(7), 819-823.

Jacob, M., Varughese, K. T., and Thomas, S. (2005). “Water sorption studies of hybrid biofiber-reinforced natural rubber biocomposites,” Biomacromolecules 6(6), 2969-2979.

Liu, M., Liu, Z., Ding, S., Li, S., and Zhang, L. (2003). “Graft copolymerization of oleic acid onto low-density polyethylene in the molten state,” Journal of Applied Polymer Science 90(12), 3299-3204.

Lu, J. Z., Negulescu, J. I., and Wu, Q. (2005). “Maleated wood-fiber/high-density polyethylene composites: Coupling mechanisms and interfacial characterization,” Composite Interfaces, 12(1-2), 125-140.



Mohanty, S., Verma, S. K., and Nayak, S. K. (2006). “Dynamic mechanical and thermal properties of MAPE treated jute/HDPE composites,” Composites Science and Technology 66, 538-547.

Naik, J. B., and Mishra, S. (2007). “Esterification effect of maleic anhydride on swelling properties of natural fiber/high density polyethylene composites,” Journal of Applied Polymer Science 106(4), 2571-2574.

Nishino, T., Hirao, K., Kotera, M., Nakamae, K., and Inagaki, H. (2003). “Kenaf reinforced biodegradable composite,” Composites Science and Technology 63(9), 1281-1286.

Oksman, K., and Clemons, C. (1998). “Mechanical properties and morphology of impact modified polypropylene–wood flour composites,” Journal of Applied Polymer Science 67(9), 1503-1513.

Article submitted: April 5, 2011; Peer review completed: June 28, 2011; Revised version received and accepted: July 6, 2011; Published: July 8, 2011.

MECHANICAL PROPERTIES AND WATER · PDF filepolyethylene (rHDPE) /natural rubber (NR) blends...

Documents

Transcript of MECHANICAL PROPERTIES AND WATER · PDF filepolyethylene (rHDPE) /natural rubber (NR) blends...